Abrasive disk

ABSTRACT

THIS DISCLOSURE DESCRIBES AN ABRASIVE DISK AND A METHOD OF MAKING AN ABRASIVE DISK WHICH INCLUDES IMPREGNATING A COMPRESSIBLE POROUS BACKING SHEET MATRIX HAVING A PLURALITY OF SEGMENTS DEFINING VOIDS WITH A BONDING MATERIAL WHICH COATS THE SEGMENTS TO FORM A BACKING SHEET. THE BACKING SHEET IS THEN PLACED NEXT TO A HUB AND THE TWO ARE HEATED AND SQUEEZED TO COMPRESS THE BACKING SHEET AND CAUSE THE BONDING MATERIAL TO FLOW TO BOND THE HUB TO THE BACKING SHEET.

v Us. ci. s1-sss United States Patent O 3,561,938 ABRASIWE DISK Alecir Block and Keith R. Whitcomb, Los Angeles, Calif., assignors to Merit Products, Inc., Los Angeles, Calif., a corporation of California Filed Feb. 5, 1968, Ser. No. 702,945 Int. Cl. B24d 17/00 5 Claims ABSTRACT OF THE DlSCLOSURE This disclosure describes an abrasive disk and a method of making an abrasive disk which includes impregnating a compressible porous backing sheet matrix having a plurality of segments defining voids with a bonding material which coats the segments to form a backing sheet. The backing sheet is then placed next to a hub and the two are heated and squeezed to compress the backing sheet and cause the bonding material to ow to bond the hub to the backing sheet.

BACKGROUND OF THE INVENTION This invention relates to an abrasive disk drivable by a rotary drive shaft for performing various abrading operations. An abrasive disk of the type to which the present invention relates typically includes abrasive material mounted on a suitable backing member or sheet. A hub or button is adhesively mounted on the backing sheet and is connectable to the rotary drive shaft to drive the abrasive disk.

It will be readily appreciated that in actual use of the disk the connection between the hub and the remainder of the abrasive disk is subjected to substantial torque loads. Furthermore, in use and handling of the disk, the connection between the hub and the remainder of the disk is subjected to bending or iiexing forces which tend to break or peel the hub away from the remainder of the disk. Failure of the abrasive disk under torque, bending, or other loads has been a major problem with prior art abrasive disks.

Hubs of the type used with abrasive disks typically have a flange which is adhesively secured to the backing sheet. lt is desirable to construct the hub from a plastic material such as nylon because plastic is relatively strong, inexpensive, and can be easily formed into the rather intricate shape necessary for the hub. However, it is very diiiicult to securely bond the nylon to the backing sheet. In an attempt to overcome this problem, one prior art device includes a layer of Woven cloth having a polyvinyL chloride coating thereon. The woven cloth is adhered to a layer of abrasive cloth through an intermediate fibre layer. A metal hub is coated with polyvinylchloride and the polyvinylchloride coating on the hub and on the cloth are then welded together with heat and pressure. This prior art process is undesirable in that the metal hub cannot be snapped onto-a drive member for the abrasive disk and cannot be molded into the intricate shapes desired. In addition, the process is somewhat complex in that both the hub and the woven cloth must first be coated with polyvinylchloride.

SUMMARY OF THE INVENTION The present invention provides an abrasive disk in which the connection between the hub and the remainder of the disk is substantially strengthened and in which the problems experienced heretofore with prior art connections of this type are eliminated. This improvement results, in part, from using a porous compressible backing sheet matrix which has many segments which define voids. The matrix is initially iiexible and the segments preferably comprise fibres. To initiate the process, the fibres of the matrix are coated with a bonding material so that the bonding material partially iills the voids. The fibre coating operation can be advantageously carried out by impregnating the matrix with the bonding material, squeezing the excess bonding material from the compressible matrix and heating the matrix in an oven to evaporate the solvent from the bonding material. The matrix with the bonding material therein constitutes a porous compressible mat or backing sheet.

Next, the backing sheet is heated to make the bonding material iiowable and, while the bonding material is flowable, the backing sheet and the iiange of the hub are squeezed together. The compression of the backing sheet reduces the volume of the voids and causes the bonding material to iiow to till the reduced volume voids and to intimately contact the ange of the hub so that when the bonding material hardens the hub and the backing sheet are securely bonded together. Preferably, all of the layers of the abrasive disk are squeezed together in a single operation to cause the bonding material Within the backing sheet to bond all of the layers together. The resulting abrasive disk formed by this method may include the backing sheet with the hub and a layer of abrasive bonded to the opposite faces thereof.

The use of the porous backing sheet matrix makes it possible for the matrix to hold a veiy substantial quantity of bonding material and in the compressed condition, the bonding material forms the majority of the volume of the backing sheet. The matrix and the bonding material mutually reinforce each other to strengthen the backing sheet. Although the matrix is initially flexible, following the steps of this process, the backing sheet has very desirable strength characteristics. Preferably, the matrix is in the form of a nonwoven fibrous material. Nonwoven cloth is preferred to Woven cloth because it provides significantly increasedporosity and because its strength characteristics are nondirectional. ln addition, the inherent fuzziness of nonwoven fibrous material seems to impart additional strength to the backing sheet-to-hub bond.

Another feature of the present invention is that a strong hub to backing sheet lbond is obtained even though the hub is constructed entirely of a plastic material such as nylon. As the hub is constructed entirely of plastic material, formation thereof into the intricate shapes necessary for the hub is facilitated and the plastic hub can easily be attached to a rotatable driving member with snap action. Formation of the plastic hub is much easier than formation of a metal hub and applying a coating of plastic material to the metal hub.

' Almost any bonding material which will form a strong hub to backing sheet bond can be used. According to one aspect of the present invention, the bonding material contains suiiicient quantities of a plastic material, which is sufficiently similar to the plastic material of the hub, so that the two plastic materials will fuse when heated. The result is a strong chemical bond or link between the hub and the backing sheet. According to another aspect of this invention, the bonding material is in the form of an epoxy resin of a type which will form a strong bond between the plastic hub and the backing sheet.

To further assure that a strong bond will be provided, a solvent may be applied to the iiange of the hub prior to squeezing the hub and backing sheet together. The solvent dissolves a surface region of the iiange of the hub and gives it a gummy feeling and appearance and makes the flange much more conductive to bonding to the backing sheet. Another advantage of the solvent is that With the surface region of the flange at least partially dissolved, a strong bond is obtained without heating the hub to a high enough temperature to melt or fuse it to the bonding material. Thus, although the hub may be constructed of a high melting point nylon, the bonding operation may be carried out at a relatively low temperature.

The present invention also teaches forming the flange of the hub in a special manner to mechanically enhance cooperation between the bonding material and the flange. The flange may be formed in several different ways to 21C- complish this result. First, the flange may define pockets into which some of the bonding material may be received. Thus, when the bonding material hardens, it forms an abutment or key lock which resists relative rotation between the hub and the remainder of the disk. As a supplement to the pockets, or in lieu thereof, the periphery of the flange may `be noncircular with respect to the axis of rotation of the hub and the disk. As the hub is connectable to the rotary drive member, the axis of rotation extends axially through the hub, and thus, any flange which is not circular with reference to the rotational axis would cooperate with the bonding material to resist relative rotation between the hub and the remainder of the disk. In a preferred form of the hub, the flange includes a plurality of radially extending projections in between which the bonding material may be received to, in effect, key-lock the hub to the backing sheet.

The invention, both as to its organization and method of operation together with fur-ther features and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying illustrative drawing.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view through an abrasive disk constructed in accordance with the teachings of this invention, with the disk being drivingly connected to a rotary drive shaft.

FIG. 2 is a top plan view of the hub.

FIG. 3 is an enlarged fragmentary sectional view taken on a radially extending plane through one of the radially extending projections ofthe hub and showing the layers of the abrasive disk adjacent the periphery of the flange.

FIG. 4 is a diagrammatic elevational view of a preferred form of backing sheet matrix.

FIG. 5 illustrates a preferred manner of Coating the fibres of the matrix with a bonding material.

FIG. 6 is a diagrammatic view similar to FIG. 4 illustrating the backing sheet in its uncompressed state.

FIG. 7 is a sectional view illustrating a preferred method of bonding the various layers of the abrasive disk together and for clarity showing the layers of greatly increased thickness.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings and in particular to FIG. l thereof reference numeral 11 designates an abrasive disk constructed in accordance with the teachings of this invention. Generally the abrasive disk 11, which may be circular in plan includes a layer of abrasive 13, a backing sheet 15, a cover sheet 17, and a hub 19. The hub 19 has an attachment portion 21 and a peripheral flange 23 which is sandwiched between and secured to the backing sheet 15 and the cover sheet 17. The cover sheet 17 has a central opening 25 therethrough through which the attachment portion 21 of the hub 19 projects. The attachment portion 21 is connectable to a rotary drive `shaft 27 by any suitable conventional means 29. Thus, the abrasive disk 11 is mounted for rotation about a rotational axis which extends centrally through the attachment portion 21 and the disk. The disk 11 is supported during an abrading operation by any suitable conventional wheel 31, which is also rotatably mounted on the drive shaft 27.

With reference to FIG. 2, the hub 19 is preferably formed entirely of a strong lightweight plastic material such as nylon. The attachment portion 21 is generally circular in plan and includes a plurality of circularly arranged fingers 33 which project generally transversely of the flange 23. These fingers are somewhat flexible and serve to connect to the hub 19 to the shaft 27 in a conventional manner. For example, each of the fingers 33 may have a radially inwardly extending flange (not shown) for assisting in attaching the hub 19 to the drive shaft 27 with a snap action. The fingers 33 are separted by slots 35 and the attachment portion 21 has a central aperture 37 extending therethrough.

The flange 23 has a plurality of radially extending irregularly shaped fingers 39 which are spaced circumferentially by grooves or pockets 41. The periphery of the flange 23 has an irregular shape and is materially lengthened by the presence of the grooves 41. Each of the grooves 41 is arcuate and preferably generally forms a portion of a circle so that each of the fingers 39 has a pair of oppositely directed tips 43. The periphery of the flange 23 may be generally circular except for the grooves 41 and concentric with the attachment portion 21. As shown in FIG. 3, each of the fingers 39 is tapered to become thinner as it extends radially outwardly from the attachment portion 21.

The backing sheet 15 includes a porous backing sheet matrix filled with a suitable bonding material as described more particularly hereinbelow. As shown in FIG. 3, the bonding material extends upwardly from the backing sheet 15 to form a hooklike element or keylock 45 which extends over an upper surface 47 of the flange 23. The hooklike elements l45 assist in securely holding the hub 19 to the backing sheet 15. The bonding material also extends along an inner face 49 of the flange 23 to securely bond the latter to the backing sheet 15.

The cover sheet 17 can be of any material 'which can be bonded to the backing sheet 15 and to the hub 19. Although the cover sheet 17 can be omitted, one purpose of the cover sheet is to cover the periphery of the flange 23 of the hub 19 as shown in FIG. 3 to thereby reduce the tendency of the flange to peel away from the backing sheet 15. Preferably the cover sheet 17 has some strength to thereby further increase the strength of the connection between the sheets 15 and 17 and the hub 19. Although other materials may be utilized, in the embodiment illustrated, the cover sheet 17 is constructed of a large mesh, woven fabric.

The layer of abrasive 13 can be of any suitable design and in the embodiment illustrated is an abrasive cloth. Except for the opening 25 in the cover sheet 17, all of the layers 13, 15 and 17 are preferably coextensive and define a circular periphery for the disk 11.

The abrasive disk shown in FIGS. 1-3 may be made according to the method illustrated in FIGS. 4-7. FIG. 4 illustrates a backing sheet matrix 51 which ultimately forms a portion of the backing sheet 15 and which is preferably in the form of a nonwoven, compressive, porous, long fibre mat. As shown diagrammatically in FIG. 4, the mat 51 includes numerous fibres 53, which may be polyester fibres, extending in random fashion throughout the matrix and defining therebetween many relatively large volume voids 55. The matrix 51 is flexible and, because the fibres S3 extend randomly throughout, its strength properties are nondirectional. The voids 55 account for a major volume of the matrix 51 and the fibres 53 are flexible so that the matrix 51 can be compressed substantially to a much thinner Width. The fibres 53 extend to the outer surface of the matrix 51 to give the matrix a fuzzy appearance. By way of example, the matrix 51 may be a nonwoven porous polyester long-fibre mat which is sold under the trademark Lantuck The first step of the process is to coat the fibres 53 with a bonding material and this can be accomplished as shown in FIG. 5 by immersing the matrix 51 in bonding material 57 which is in liquid form. The immersion irnpregnates the matrix 51 with the bonding material 57 and the voids 55 thereof are substantially full of the bonding material. The matrix 51 is then run through a pair of rolls 59 which squeeze some of the excess bonding material from the matrix 51. As the bonding material will usually contain a solvent, the next step of the process is to pass the matrix 51 through an oven 61 in which the matrix is heated to evaporate the solvent from the bonding material. The article leaving the oven is in the form of an uncompressed backing sheet 63 which is illustrated schematically in FIG. 6. The backing sheet 63 has the libres 53 thereof coated with the bonding material 57 as illustrated. The bonding material 57 lls a portion of the voids 55, but leaves a substantial volume of the voids unfilled.

The bonding material 57 may be of the type which produces a fusion or chemical type bond or of the type which produces primarily an adhesive or mechanical type bond. Broadly, a chemical bond may be obtained by utilizing a bonding material which contains a suflicient quantity of plastic material suiciently similar to the plastic material of which the hub is constructed, so that the two plastic materials will fuse when heated, and upon cooling, harden to form a strong bond or weld. As any two identical thermoplastic materials can be welded to each other by heating the thermoplastic material suiciently and then allowing them to cool, the bonding material may include a substantial quantity of plastic material identical to the plastic material from which the hub is constructed. By way of example, the following bonding material has been found suitable for use with a hub which is constructed of Du Pont nylon 101. The bonding material may be produced by mixing a type of nylon known as Elvamide 8061 produced by Du Pont with suitable quantities of a solvent such as methanol or ethanol. To give the dissolved Elvamide sufficient body to adhere to the fibres 53 in sucient quantity, a thickening agent may be added in the quantity necessary to give the bonding material the desired consistency, for adhering to the fibres in the desired quantity. The thickening agent is preferably a brous additive such as woodour which provides many cellulose fibres to which the bonding material may adhere to after the solvent has been evaporated in the oven 61.

By way of example, the bonding material 57 may be produced by mixing 28 lbs. of methanol, 5 lbs. of tap water, 9 lbs. of Elvamide pellets, and 2.2. oz. of woodflour. The woodtlour may be of the type known as Solka Floc which is sold by McKesson-Robins. This mixture is elevated to a temperature of 120 F. and agitated by a rotary paddle for approximately one hour or until all of the ingredients are dissolved. If desired, the bonding material may be colored with a dye.

If an adhesive or a mechanical type bond is desired, the bonding material 57 may be in the form of an epoxy or thermosetting resin that will bond to the material of the hub and will also stick to the abrasive 13. For example, the bonding material of the epoxy resin type may be produced by adding lv lbs. of toluene, 20 lbs. of isopropanol, 24 lbs. of No. 540X90 Ciba epoxy resin, 1l lbs. of 815X70 Ciba polyamide and 20 lbs. of talc in the above order to a mechanical type agitator. The ingredients are then mixed or agitated at room temperature for approximately minutes or until all of the ingredients are thoroughly mixed or dissolved. ln the example given above, the toluene and isopropanol serve as a solvent and the polyamide is a curing agent. The talc acts as a thickening agent to give the bonding material sufficient body so that it Iwill remain in the matrix 51 in sufcient quantity.

Once the backing sheet 63 has been suitably prepared, the abrasive disk 11 may be simply formed in a one-step lamination process, although, if desired, the disk could be formed in a series of steps carried out sequentially. As shown in FIG. 7, the lamination process is preferably carried out between an upper plate 65 and a lower plate 67. The lower plate 67 has a plurality of apertures 69 (only one being shown in FIG. 7) each of which is sized to receive and retain the attachment portion 21 of one of the hubs 19 against significant lateral movement. The upper plate 65 preferably carries a plurality of heating elements 71.

Initially, a cover sheet 73 which is large enough to provide many of the cover sheets 17 is positioned on the upper surface of the lower plate 67 and the apertures 25 may be formed therein if they have not been preformed. Next, the hubs 19 are positioned with the attachment portion 21 of each of the hubs projecting into one of the apertures 69 and with the flange 23 of each of the hubs resting on a region of the cover sheet 73 immediately surrounding the apertures 25 therein. Next, the backing sheet 63 and an abrasive layer 7S, both of which have large surface areas, are laid sequentially on the lower plate 67 as shown in FIG. 7.

With the heating element 71 in operation the upper plate 65 is moved downwardly to engage the abrasive layer 75 and to squeeze the entire lamination between the plates 65 and 67. The force of compression across the thickness of the lamination shown in FIG. 7 is sufcient to compress the backing sheet 63 to reduce the volume of the voids 55 a substantial amount. The heat from the heating element 71 is suicient to cause the bonding material 57 to flow to fill the reduced volume voids and to intimately contact the lower or inner face 45 of the flange 23. Simultaneously, the bonding material 57 ows to contact the inner face of the abrasive sheet 75 and the cover sheet 17. The ow of the bonding material 57 may also operate to form the hooklike element 47 (FIG. 3). The lamination is held between the plates 65 and 67 momentarily and then allowed to cool to set or harden the bonding material to rmly secure all of the layers of lamination together with the backing sheet being retained in a compressed condition by the bonding material. The large lamination may then be cut to form a number of the abrasive disks 11.

To further improve the bond between the hub 19 and the backing sheet 63, it is preferred to apply a solvent to the inner face 49 of the flange 23 prior to squeezing of the backing sheet 63 against the hub. The solvent should be of a type suitable to dissolve the surface region of the inner face 49 to make it gummy or tacky and may be used whether the bonding material 57 is of the type which will form a chemical or mechanical bond with the hub 19. By way of example, when the hub is constructed of Du Pont nylon 101, the solvent may be resorcinal formic acid or phenol. By way of example, a suitable solvent can be prepared by dissolving resorcinol crystals in a suitable solvent such as an alcohol reagent. For example, the resorcinol crystals and the alcohol reagent may be mixed at room temperature at a one-to-one ratio of a weight basis.

The bond between the backing sheet 63 and the abrasive cloth can be improved by scarifying the inner face, i.e., the face contiguous the backing sheet, of the abrasive cloth to form an irregular roughened surface to which the bonding material will more readily adhere. This can be accomplished by rubbing the inner face of the abrasive cloth with a wet cloth. The moisture in the cloth serves to break down the water soluble material which often appears on the inner face of the abrasive cloth.

Although exemplary embodiments ofthe invention have been shown and described, many changes, modifications, and substitutions may be made by one having ordinary skill in the art without necessarily departing from the spirit and scope of this invention.

What is claimed is:

1. An abrasive disk consisting of a laminated plastic assembly having an attachment face connectable to a drive shaft having an axis of rotation, and an opposite abrasive face, which disk comprises:

a unitary molded plastic hub formed with a flange disposed around said axis and formed with some edge surfaces radial with respect to said axis to transmit rotational drive to said laminated plastic assembly, and

an attachment portion comprised of a ring of independent ingers projecting from the attachment side of said flange, and disposed around said axis to make snap-on driving engagement with said shaft;

a backing sheet disk of substantially greater radius than said flange of said hub laminated to said flange coaxial with said axis, said backing sheet being formed of a fibrous material with many voids between fibers to render said sheet porous and compressible, and said backing sheet being compressed at the surface contacting said iange to form protuberances mating with the edge surfaces of said ange;

an abrasive sheet disk of substantially the same radius as said backing sheet and laminated to said backing sheet, said abrasive sheet disk having an abrasive surface comprising the abrasive face of said abrasive disk; and

a hardened bonding plastic extending through the voids of said backing sheet disk and its protuberances to make bonding contact with said plastic hub and said abrasive sheet disk.

2. An abrasive disk as described in claim 1, in which said laminated assembly includes a cover sheet disk laminated to the attachment face side of said ange and said backing sheet disk by said hardened bonding plastic.

3. An abrasive disk as described in claim 1, in which said ange has its edges shaped to form pockets into which said backing sheet protrusions and said bonding material are received to transmit rotational drive to said assembly.

4. An abrasive disk as described in claim 1, in which said hub, the fibers of said backing sheet disk, and said `bonding plastic, are all of similar plastic materials forming a laminated plastic assembly in which all three are fused into each other at their adjacent surfaces.

5. An abrasive disk as described in claim 1, in which said hub, the iibers of said backing sheet disk, and said bonding plastic, are all forms of nylon capable of forming strong bonding to each other in said laminated assembly.

References Cited UNITED STATES PATENTS 2,784,132 3/1957 Maisel 51-298.16X 2,972,554 2/1961 Y Muskat et al 5l-296.6X 3,041,797 7/1962 Mofliy 51-378 3,082,582 3/1963 Jeske 51-358 3,169,899 2/ 1965 Steuber 51-298.l6X 3,333,371 8/1967 Pratt et al. 51--358 3,395,417 8/1968 Matouka 51-358 OTHELL M. SIMPSON, Primary Examiner 

